Short wave converter



May 14, 1935.

H. M. LEWIS SHORT WAVE CONVERTER Filed Sept. 25, 193]. 3 Sheets-Sheet l8 m H T! N y a mm n v A d i d m m fi 29E w v 1 y 1935- H. M. LEWIS2,001,277

SHORT WAVE CONVERTER Filed Sept. 25, 1931 3 Sheets-Sheet 2 lNVENTORHarald M/fifr {FM/$- ATTO R N EYS y 935- H. M. LEWIS 2,001,277

SHORT WAVE CONVERTER ATTORNEY Patented May 14, 1935 UNITED STATES2,001,277 SHORT WAVE CONVERTER Harold Miller Lewis, Douglaston, N. Y.,assignor to Hazeltine Corporation Application September 25, 1931, SerialNo. 565,024

21 Claims.

The present invention relates to a tuning system, or, more particularly,to such a system for use in a short wave receiving apparatus. Exem-,

plary of such a system is that used in a. short wave converter.

A short wave converter is an apparatus which, when used in conjunctionwith any broadcast receiver, permits the reception of short wave signalsby the said broadcast receiver. The converter comprises an oscillatorand modulator, by which the short wave signal currents are convertedinto currents of a frequency within the tuning range of the broadcastreceiver. The current of this frequency, which frequency will bereferred to hereinafter as the intermediate frequency, is amplified,detected and reproduced by the broadcast receiver.

The frequency range covered by the short wave band is approximately from1500 kc. (200 meters) to 20,000 kc. (15 meters). This range offrequencies is so great that it is not practical to tune a circuitthrough the entire range by the variation of a single tuning element.Some arrangement must be provided for changing both of the frequencydetermining elements; that is, both the inductance and the capacity. Inaccordance with the usual practice the tuning is actually done byvarying the capacity of a variable condenser, and the inductance ischanged in steps to permit the condenser to tune the circuit throughoutthe various portions of the range.

It is common practice to divide the short wave band into several bandswhich will be referred to in this'application as the short wave band,the middle wave band", and the "long wave band."

The inductances used in tuning the radio frequency circuits of the shortwave receiver, or the radio frequency circuit and oscillator circuits ofa. converter, are usually wound on removable forms commonly known asplug-in" coils, which coils are changed when desiring to go from one ofthe short wave bands to another. A system of this type has thedisadvantages that it is expensive to manufacture and requires shiftingof coils when operating.

Various systems have been proposed by which the inductance of the tuningcoils is changed in steps by means of switches. However, the leads andswitch mechanisms introduce capacities which considerably lessen therange of the tuning condensers, and usually the resulting large numberof points to be switched has condemned this system.

Furthermore, considerable dimculty is experienced in constructing anoscillator capable of covering such a broad range of frequencies, asthere is a considerable difference in the feed- 7 back coupling neededat the two ends of the short wave band.

It is the object of the present invention to overcome the above noteddifficultiesand provide a system in which the inductance values of asingle winding may be varied in steps by providing a system in which theleads required for changing the inductances are relatively short andhave negligible capacity eflects. It is a further object of thisinvention to provide an oscillator coupling system havinga simplestructure, not involving the use of moving parts, by which the couplingeffect may be simultaneously'altered as the frequency determininginductance is changed, to permit the oscillator to oscillate eifectivelythroughout the entire short wave band. v

These and further objects of this invention will become apparent fromthe" following spec'- ification taken in connection withthe appendedclaims and drawings. t

In accomplishing the objects of the present invention the inductance ofthe frequency deter mining circuit of the converter oscillator is pro-5vided with a switch for short-circuiting the long wave portions thereofand long wave and middle wave portions thereof, when operating theoscillator to receive signals in the middle wave band and short waveband, respectively. Dual magnetic and capacitative feed-back, couplingsare provided between the platecircuit of the oscillator and the gridcoil when operating within the middle wave band; When operating in thelong wave band the inductive' coupling is negligible, and the feed-backis essentially through the capacitative coupling betweenfthe plate andgrid circuits. When operatingin the shortwave band the capacitativecouplingeffect becomes negligible, whereas the coupling between thecircuits due to the inductive coupling, is considerable- Provision isalso made for obtaining a uniform coupling between the antenna circuitand the input of the modulator. A straight inductive coupling isutilized when receiving signals within the short wave and middle wave.band. When operating in the long waveband an auto transformer effect isobtained byconnecting the an--. tenna circuit to include'i a portion ofthelong wave section of the grid inductance.

The modulator and oscillator windings are so arranged relative to theswitches for short-cir cuiting their unused portions and relative to thegrids of the modulator and oscillator tubes thatthe leads, particularlywhen the converter is operating in the short wave band, are as short aspossible.

In order to permit the continuous rotation of the tuning dial in eitherdirection to progressively tune the converter .through the entire band,the condensers used 1n both the modulator input and oscillator circuitsare each provided with double stators and double rotors so constructedthat when the capacity between one of the pair of rotors and stators ismaximum, that between the other pair of rotors and stators is minimum.\This feature is covered more particularly in application of William A.MacDonald for Condensers, Serial No. 564,997, filed concurrentlyherewith.

Switching means are provided, operated simultaneously with the switchesfor short-circuiting the unused portions of the tuning inductances, forconnecting the appropriate sections of the condensers.

Series condensers are provided for connection in the oscillation circuitfor each of the bands and are appropriately connected in circuit by aswitch operated together with the previously mentioned switches, whenthe range of the converter is shifted from one band to the other. Thepadding condensers for the section of the oscillator tuning condenser,which is used for the middle wave band, is provided in shunt with thissection. A condenser is connected from the middle wave band tap of theinductance to the stator of the condenser, so that when the entiretuning inductance is in use this condenser may act as a paddingcondenser for the long wave v band. This condenser is then essentiallyin shunt with the section of the variable condenser in use.

When the long wave section of the inductance is short-circuited,however, as when operating inthe middle wave band, this condenser is inr parallel with-the series condenser in use at that time. The condense!shaft has an indicator dial geared thereto so arranged that it rotates acomplete revolution for each half revolution of the'.

condenser shaft. This dial has thereon three indicating scales, theouter scale being for indi cating the frequencies in the short waveband, and the inner scale being for indicating the frequencies in thelong wave band. The scales pass by indicator lights placed behind thedial within a compartment which permits illumination of but a singlescale by each lamp, and a. switch operated simultaneously with the wavechanging switches operates to light the appropriate scale. A fulldescription of this feature of the present invention is given inanapplication of Harold Miller Lewis for Tuning scale, Serial No. 565,027,filed September 25, 1931, Patent No. 1,987,857 dated January 15, 1935.

In order to permit the operation of a single control knob to control thefrequency oi. reception, regardless of which of the three bands theconverter is operating in, there is provided a gang switch mechanismoperated by the condenser control knob at the appropriate instant,

as the dial is rotated from one to the other of the frequency bands.This feature of the present.

ment, Serial No. 565,026, filed concurrently herev with.

It can thus be seen that an arrangement has spond is automaticallyindicated at all times as the set is tuned. y

In order to prevent the reception of broadcast signals by the receiverused in conjunction with the converter, the leads between the converter,as well as the converter itself, are completely shielded. The antennainput of the converter contains a trap circuit to prevent currents ofundesired frequency being impressed upon the input of the modulator andamplified thereby. The plate supply of the modulator contains a tuned'radio frequency choke which is tuned roughly to the intermediatefrequency and thereby tends to bypass currents of frequencies differinggreatly therefrom which have been received in the converter. Thefulldetails of this portion of the present invention are given in anapplication of Harold Miller Lewis for Short wave receiver arrangement,Serial No. 565,025, filed concurrently herewith.

Attention is now invited to the accompanying drawings in which:

Fig. 1 is a circuit diagram of the converter em- Figs. 7 and 8 representthe secondary and primary windings respectively of the antenna couplingtransformer used in the converter comprising the present invention, andi Figs. 9 and 10 represent the secondary and primary respectively of theoscillator coil.

Referring now to Fig. 1, the antenna circuit includes the antenna III,the ground I I, the trap circuit I2, comprising the inductance I3 andcondenser Il, the primary winding I5, and a portion of the secondarywinding I6. The inductance I 3 and. the condenser ll of the trap circuitI2 are so proportioned that said circuit is resonant to the intermediatefrequency produced by the short wave converter. The input circuit of theconverter is connected to the grid of modulator device I'I, which may beany thermionic tube,

though that shown is of the screen grid type. The input circuit is tunedby means of the condenser 2I which may be a double condenser employing,as shown, a single rotor and two stators so arranged that the capacityobtained between the rotor and one stato'r is maximum, when the capacitybetween the rotor and the other stator is minimum. The connections tothe stators are controlled by means of the switch 23. actual condenserincludes two stators and two rotors, so arranged that when one rotor isentirely within its stator, the other rotor is entirely out of itsstator. This is fully described inthe application of W. .A. MacDonald,Serial 564,997,

mentioned above. The function of the condenser and switch arrangementwill be explained later.

The tapped secondary I6 is connected by means of switch 24, so that anyof the tapped portions of the secondary may be included in the inputcircuit, The switch is so connected that the un- The.

used portions of the winding are short-circulted.

For producing the heterodyne frequency for combining with the incomingsignal and thus producing the intermediate frequency, there is providedthe oscillator 25. This oscillator tube is of the single grid type andincludes in its grid circuit the secondary 40 of the oscillationtransformer, the primary 42 of which is connected in the plate circuitwhich includes stopping condenser 43. The secondary 40 is a tappedwinding similar to I6 of the antenna transformer, and the connections tosaid secondary are controlled by means of switch 34. The grid return ofthe oscillation circuit is completed through the biasing resistor 21,which is connected to the cathode of the tube 25. The frequency of theoscillation circuit is determined by means of condenser 3|, which issimilar to condenser 2|, and is connected to be operated therewith in auni-control manner by means of the control knob 22 associated with theindicator dial 25.

The connections to the two continuously variable portions of thecondenser 3| are controlled by means of switch 33.

Padding condznsers MM and 4| S are provided across the two portions ofcondenser, as shown, for the purpose of aligning the oscillation circuitwith .the input of modulator I! in the middle wave range and short waverange, respectively. Padding condenser 41L is connected across the longwave portion of the inductance winding 40, so that when the switch 34 ison contact L this condenser is practically in shunt with the condensers3| and MS for adjusting the alignment in the long wave range. When theswitch 34 is on contact M, the condenser 4| L is in shunt withcondensers 31 and 31', and the total series capacity is at that time thesum of these three condensers.

In series with condenser 31 is provided a series capacity which isvariable in steps, comprising condensers 36, 31 and 38, the connectionsto which are controlled by means of the switch 35. Each of thesecondensers is provided with the padding condenser 36', 31, or 38,respectively, for the purpose of correcting the alignment of oscillatorcircuit with the modulator input in the various frequency bands. In themiddle frequency band, as has just been stated, the condenser 41L is inshunt with 31 and 31'. Coupling coils 44 and 45 coupled to the middleand long wave portions of the secondary 40, respectively, are includedin the cathode circuit of the modulator IT. This circuit also includesthe biasing resistor 46 shunted by by-pass condenser 41 for the purposeof causing tube l 7 to act as a modulator.

The plate and screen grid potential are provided by means of the powersupply source which, as shown, is of the ordinary double wave rectifierand filter type. This power supply also provides heater lighting currentfor heating the cathodes of tubes l1 and 25. A resistor 29 is includedin the plate lead of the oscillator for the purpose of reducing theplate potential thereof.

As shown, the dial 26 includes three scales, 25a, 26b, and 26c,these'scales covering the short wave band, middle wave band, and longwave band, respectively.

It is to be noted that in order to get better spacing of the frequencyindicators, the short wave scale is placed in the outer position on thedial 26, as the condenser motion to get the frequency separationrequired to separate the various stations is less in the short wave bandthan it is in the long wave band.

For the purpose of indicating in which of the frequency ranges theconverter is operating, each of the scales is provided with one of theilluminating lights ll-a, Hb, or '|I-c, controlled by means of switch 39to light them when tuning through the short wave band, middle wave band,and long wave band, respectively.

Switches 23, 24, 33, 34, and 30 are so arranged as to be simultaneouslyoperated and also to be actuated by the control knob 22 as thecondensers are tuned through the limiting capacities for one of thefrequency bands. Thus, the rotation of the control knob 22 results inthe actuation of the switches 23 and 33, resulting in switching of theconnections to condensers 2| and 3|, respectively, to give the oppositecapacity extreme for the modulator and oscillator circuits. Switch 33 issimultaneously operated changing the lighting of the indicating lightsand thus indicating the change in the frequency band by changing theindication from one to another of the scales. The specific means foractuating the switches constitute no part of the present invention, butare described fully in application of Harold Miller Lewis, for Switchingarrangement, Serial No. 565,026, filed concurrently herewith.

Included in the plate supply to the modulator I1 is the inductance 50.

capacity 5|, or an actual condenser may be placed in shunt therewith.The inductance and capacity, however, are so proportioned thatfrequencies other than the desired intermediate frequency 3 will beby-passed. I

A connection from the output of modulator IT is made through condenser52 and lead 53 to the antenna binding post of the receiver 51. Thisconnection is made through a shielded cable 54, which may, for example,be a BX cable, from the walls of which the lead 53 is spaced by means ofbakelite spacers 55. Also connected through the cable 54 is the groundconnection 55, which is connected to the ground binding post of receiver51. The capacity 52 and the inherent capacity between the leads 53 and55 are so pro-- portioned that they constitute a dummy antenna toproperly load the modulator H, arid to prevent misalignment of the inputof receiver 51. Switch 59 is provided between the antenna 10 and thelead 53 by means of which the antenna may be directly connected to theinput of the receiver 51 when it is desired to receive signals in thebroadcast band directly on receiver 51.

The receiver 51 may be of any well known type, and is provided with theusual sound reproducing device 58. The specific details of neither 5?nor 58 constitute any part of the present invention.

The receiver is tuned to the intermediate fre quency which it is desiredto utilize, preferably 1,000 kc. The direct reception of signals of1,000 kc. when the set is being operated to receive short wave signalsby means of the converter, is prevented by means of the shielded cable54. The modulator is prevented from acting as an amplifier of signals of1,000 kc. frequency by means of trap circuit l2. Any signals of afrequency other than 1,000 kc. in the .output of modulator l'l would beby-passed through the inductive 50. It is thus seen that a number ofprovisions have been made to prevent the interference of broadcastsignals with the short wave signals being received by means of theconverter.

This inductance may have a high inherent capacity as indicated by InFig. 2, to which attention is now invited, the circuit shown in Fig. 1is again represented, except that'the switches have been eliminated, theconnections beingmade as if the converter were tuned to some frequencywithin the long wave band. In this circuit the high potential isrepresented as being supplied by means of the directcurrent source 80,and the screen grid potential of the device I! is obtained therefrom byincluding a resistor 8| in the screen grid circuit. The output of theoscillator circuit herein represented as 83 is fed to the cathode leadof the modulator I! which, as has been described, is biased for gridbias detection. The incoming signal is fed through the oscillatorycircuit 84 to the input of tube I I, which by means of the biasingresistor 46 operates as a rectifier or modulator, and thereby producesin its output circuit a distorted wave form from which a current of theintermediate frequency can be selected and supplied through thecondenser 52 to the terminals A and G of the radio broadcast receiver.

It is to be noted that frequencies other than the intermediate frequencyfor which the radio broadcast receiver is to be adjusted are by-passedthrough the inductance 50, whereas this inductance and its inherentcapacity form a high impedance path relative to currents of theintermediate frequency.

As previously stated, the circuit l2 acts to prevent currents of theintermediate frequency being received over the antenna l and amplifiedby the modulator l1, and the shielding of the lead 53 prevents a directpick-up between the output of the device l1 and the input of the radiobroadcast.

receiver.

The oscillator circuit 83 contains, as can be seen, the usual seriescondenser 38 in series with the tuning condenser 3|, by means of whichthe circuit 83 is made to respond to a frequency continuously differingfrom the frequency to which circuit 84 responds by the amount of theintermediate frequency as the circuits are tuned in a uni-controlmanner.

Figs. 3 and 4 illustrate the means by which the single oscillationtransformer is made to cover the considerable frequency range requiredof this type of equipment. The various portions of the inductance 40 aretuned by the respective parts of the condenser 3| and thus constitute atuned grid circuit.

In order to provide the offset frequency and thus permit alignmentbetween the condensers 3| and 2| to permit ganging, a series condenser36, 31 or 38 is provided. This condenser has the dual function ofassisting the alignment and of permitting capacitative feed-back action.The introduction of this capacity in the grid return requires a resistor21 to prevent the grid from floating and to act as a grid bias resistor.

More specifically, Fig. 3 shows the action on the circuit when it isoperating in the short wave and middle wave band. The used portion ofthe inductance40 in these bands is relativelysmall and there isconsiderable coupling efiect between the feed-back'inductance 42 andinductance 40. This is particularly true in the short wave band.

In the short wave band the capacitative feedback coupling is,negligible. In the middle wave band, however, the capacitative feed-backaction is considerable. The inductive feed-back action between 42 and 40is less within this range, and the two couplings are so arranged as togive practically uniform operation throughout the middle frequency band.

Referring particularly to Fig. 4, in which'the.

circuit represents the action of the oscillator circuit when operated inthe long wave band, the inductive coupling between the coils 42 and 40is negligible, and the oscillator is of the capacity coupled typeutilizing the series capacity 38.

Fig. 4-also represents the padding capacity arrangement. As can be seenfrom Fig. 1, the same section of the condenser 3| is utilized throughoutthe long and short wave bands. This complicates the arrangement requiredfor the padding capacity in these two bands. The usual padding condenser4|M, however, is provided for the middle frequency band. The usualpadding condenser MS is also shunted across the section of the condenserused for the long and short wave hands. This capacity is adjusted forthe short wave bands, and it has been found that it should have a verylow value. For padding the condenser 3| for operation in the long waveband, the condenser 4|L is shunted across that portion of the coil whichis in use only during operation in the long wave-band. The few turns ofwinding 40, not shunted by this condenser, are negligible when operatingwithin the long wave band, so that the condenser 4|L is essentially inparallel with the condenser 3|. However, as can be seen from Fig. 1,when the switch 34 is on contact M for operation in the middle frequencyband, the condenser 4|L is in parallel with the condensers 31 and 31',the capacities of which are, therefore, adjusted to form the totalseriescapacity which is required for producing alignment within theintermediate frequency band.

It can thus be seen that a substantially uniform feed-back coupling isobtained throughout all three of the wave bands.

An important feature of the present invention is that as there is but a.single tuning stage in the input to the modulator device, the oscillatorfrequency is the principal determinate ofthe frequency to which theconverter is set to respond. This, it can be seen, increases the tuningrange of the converter somewhat beyond what would be the case if thecondenser 2| determined the range. As an example, when using a 1,000 kc.intermediate frequency and tuning the oscillator between 3,000 and 9,000kc., which is a 3:1 ratio, the incoming frequency which can be receivedwill vary between 2,000 and 8,000 kc., giving a receiving frequencyratio of 4:1

Fig. 5 shows the modulator of Figs. 1 and 2 arranged for comparison withthe circuit shown in Fig. 6.

Fig. 6 shows an alternative form of modulator circuit in which the gridleak type of detection is used. This type of circuit gives slightlybetter sensitivity than that shown in Fig. 5, which latter is the usualgrid bias arrangement and gives a better noise level but lesssensitivity.

sistor 46 and its shunt condenser 41 have been removed, and the gridleak 46' and grid leak condenser 41' in the grid circuit of the tube I!have been substituted therefor.

Although it is clear that the specific coils for use in a converterconstructed in accordance with the present invention will depend uponthe characteristics of various other elements and upon the frequencyranges to be considered, the inductances used in covering the frequencyranges from 1,740 kc. to 19,400 kc. are shown in Figs. 7-10, and willnow be described.

Fig. '7 illustrates the antenna coupling secondary. This secondary iswound on a 1% inch form 00 In Fig. 6 the low resistance grid biasing re-3 60 and comprises 69% turns of No. 18 B & S gauge enameled wire wound20 turns per inch. The terminal BI is connected to the grid of the tube'l! and the terminal 62 is connected to the ground II. The tap 64 istaken to include 5 turns and is connected to contact S of switch 24. Thetap 65 is taken to include 20% turns and is connected to contact M ofswitch 24. The terminal 53 is connected to the antenna coil I5 and istaken 5% turns from the terminal 62.

The primary of the antenna coupling transformer is wound on inch form 61and is placed inside the form 60 of Fig. 7, and spaced therefrom bymeans of spacer 68. The winding l5 comprises 18 turns ofNo. 26 B & Sgauge enameled Wire wound 24 turns per inch. The terminals 69 and 10 areconnected to the trap circuit l2 and terminal 63 of winding l6,respectively.

The oscillator secondary winding 40, shown in Fig. 9, comprises 43%turns of No. 18 B & S gauge enameled wire wound on 1 inch form 12,

,20 turns per inch. The terminal 13 is connected to contact L of switch34 and the contact 14 is connected to the grid of oscillator tube 25.The tap 15 is taken 5 turns from the end of coil and the terminal 15 isconnected to contact S of switch 34. The terminal 16 is tapped 15%,turns from the end of the coil and is connected to contact M of switch34.

The feed-back coupling coil 42 and the modulator coupling coils 44 and45, shown in Fig. 10, are all wound on a 4 inch form 11 which is placedinside of form 12 and spaced therefrom by means of spacer 18. Thewinding 42 comp-rises 4 turns of 30 B & S gauge enameled wire closewound. Terminals 8| and 82 of winding 42 are connected to the contact Lof switch 34 and the oscillator plate condenser 43, respectively.Windings 44 and comprise 5 and 4% turns, respectively, of No. 30 B & Sgauge enameled wire close wound. Winding 45 is spaced inch from winding42, and windings 44 and 45 are spaced approximately 2 inches apart.These coils are connected in series and are connected by terminals 85and 86 to the cathode of modulator I1 and the modulator bias resistor46, respectively.

The condensers used have a maximum capacity of 195 microfarads and aminimum capacity of 19 microfarads.

Using the coils just described, the calibrated range of the converteris:

Kilocycles Meters Long wave band 1740-4180 (163-72) Middle wave band3800-9075 (7933.l) Short wave band 8650-19400 (34.8-15.5)

Certain other constants which have been found satisfactory are included:

Resistance 27=250,000 Ohms D0. 29: 25,000 do. Do. 46: 3,000 do.Condenser 36: 450 Micromicrofarads Do. 37: 1,500 do. D0. 38: 1,500 do.Do. 43: .1 Microfarads Do. 47: .1 do.

that any appropriate power supply arrangement may be substituted forthat shown.

I claim:

1. In a. vacuum tube oscillator for heterodyne reception covering abroad band of wavelengths, subdivided into a short wave band, a middlewave band, and a long wave band, a vacuum tube, a tunable grid circuitconnected to the input of said vacuum tube, and comprising inductance, avariable condenser and a condenser variable in steps, a feedback pathbetween the output of said tube and the tunable circuit, said pathincluding a second inductance, inductively coupled to said tunablecircuit, and said condenser variable in steps, and switching means forsimultaneously changing the value of said first inductance and saidcondenser variable in steps whereby feedback is primarily accomplishedby an electromagnetic coupling for the short wave band, by a combinedelectromagnetic and electrostatic coupling for the middle wave band, andby electrostatic coupling forthe long wave band.

2. An oscillation generator for generating a current of any frequency ina plurality of wave bands, comprising a vacuum tube having plate, gridand cathode electrodes, a grid circuit for determining the frequency tobe generated, connected between the grid and cathode, said circuitcomprising an adjustable inductance in series with a capacity adjustablein steps, shunted by a continuously variable condenser, a control memberfor operating said variable condenser, a feed-back circuit between plateand cathode, having an inductance magnetically coupled with said firstmentioned inductance, and including said adjustable capacity, andswitching means, operated by said control member to simultaneouslychange the values of said adjustable inductance and said adjustablecapacity.

3. In an oscillation generator of the thermionic vacuum tube type, agrid circuit, a frequency determining net work in said circuit,comprising a variable inductance, a capacity variable in steps, and acontinuously variable capacity tuning said'circuit, and a feed-backcircuit, including an inductance magnetically coupled to the firstmentioned inductance, and including said capacity variable in steps.

4. In a vacuum tube oscillator for heterodyne reception covering a broadband of wave lengths, an oscillatbr tube, grid and plate circuits forsaid tube inductively related to each other and including a commoncapacitive path, a condenser for tuning said grid circuit, and switchingmeans for altering the effective inductance of said grid circuit andsimultaneously altering the capacity of said common capacitive pathas-the wave length band to which said circuits are adapted to respond isaltered.

5. In a heterodyne receiving arrangement, an oscillator circuit in whichthe effective coupling between the grid and plate circuits issimultaneously altered as the oscillator circuit is altered to cover abroad band of frequencies, which oscillator comprises an oscillatortube, grid and plate circuits therefor, each of said circuits includingan inductance, said inductances being inductively related to each otherand having their low-potential ends connected together, connection meansfor selectively connecting the cathode of the oscillator tube to variouspoints is common to both of said circuits, means for altering saidcoupling condenser as the large changes in frequency of said oscillatorare made, and a variable condenser for tuning said grid circuit.

6. A system in accordance with claim 1, in which aplurality of variablecondensers are provided for tuning the grid circuit of said oscillator,and selecting means operated simultaneously with said switching means toselectively connect one of said condensers in said grid circuit.

7. A system in accordance with claim 1, in which a plurality of variablecondensers are provided for tuning the grid circuit of said oscillator,selecting means operated simultaneously with said switching means toselectively connect one of the said condensers in said grid circuit, andan adjustable padding condenser arranged in shunt with each of saidtuning condensers.

8. In a heterodyne receiving system, an oscillator circuit adjustable toproduce oscillations covering a broad wave length band subdivided into ashort wave band, a middle wave band and a long wave band, saidoscillator circuit comprising an oscillator tube, grid and platecircuits for said tube, said grid circuit comprising a tuned inductancehaving one end connected to the grid of said tube and having a middlewave length tap and a short wave length tap, a switch connected toselectively short-circuit the portions of said inductance below saidtaps to cause said inductance to respond to frequencies throughout themiddle wave length band or the short wave length band respectively, aseries alignment condenser for each of the wave length bands, each ofsaid condensers having one side connected to the cathod of saidoscillator tube, switching means for connecting the appropriate seriesalignment condenser in series in the grid circuit, said switching meansbeing connected to and simultaneously operable with the first-mentionedswitching means, a variable condenser connected between the grid andcathode of said tube to tune the grid circuit throughout the selectedWave length band, a resistance shunted across the series alignmentcondenser connected in series in the grid circuit between saidinductance and the cathode of said tube, and a condenser connectedbetween the middle wave length tap of said inductance and the cathodeside of said variable condenser, whereby it is alternatively placedsubstantially in shunt with said variable condenser and in shunt withthe series alignment condenser used in the middle wave band, and saidplate circuit including a stopping condenser, an inductance, and theseries alignment condenser connected in the grid circuit by saidswitching means, said last-mentioned inductance being inductivelycoupled to the grid end of said tuning inductance and connected to thelow po-' tential end thereof, whereby the coupling of said circuits isaltered as the frequency of the band is changed.

9. In a heterodyne receiving system, an oscillator circuit adjustable toproduce oscillations covering a broad wave length band, said oscillatorcomprising a tube; grid and plate circuits for said tube; said gridcircuit comprising in series a tuning inductance, a switch so connectedas to short-circuit'portions of said inductance to cause it to respondto frequencies throughout a plurality of wave length bands, an alignmentcondenser for each of the wave length bands, and switching means forconnecting the appropriate alignment condenser in series in said gridcircuit,

said switching means being simultaneously operated with said switch, anda variable condenser connected between the grid and cathode of saidtube; and said plate circuit including an inductance, inductivelycoupled to the grid end of said tuning inductance, and the alignmentcondenser connected in said grid circuit by said switching means, saidinductances and said alignment condenser being so proportioned that thecoupling between said circuits is essentially electromagnetic at theshort wave length end of the band and essentially electrostatic at thelong wave length and of the band.

10. An oscillator for covering a broad band of wave lengths, whichcomprises a vacuum tube, grid and plate circuits therefor, an inductivecoupling between said circuits, means for altering the effectiveinductance of said grid circuit to make large changes in the frequencyof said oscillator, a variable condenser in said grid circuit to varyits tuning, an auxiliary condenser and means related to said inductancealtering means for alternatively connecting said auxiliary condenser incircuit as a coupling capacity between said plate and grid circuits orsubstantially in shunt with said variable condenser.

11. A heterodyne radio-frequency system for operation over a broad waveband, comprising an oscillator including grid and plate circuits, saidcircuits each including inductively coupled inductances, and said gridcircuit including means for short-circuiting portions of the inductanceincluded therein, one of a plurality of variable condensers, and one ofa plurality of coupling condensers, all connected in series, a paddingcondenser in shunt with each of the variable condensers, means forselectively connecting one each of said plurality of variable condensersand of said plurality of coupling condensers in said grid circuit, anauxiliary condenser, and means for alternatively connecting saidauxiliary condenser in parallel with the coupling condenser thenconnected in said grid circuit or substantially in shunt with thevariable condenser at that time connected in the circuit.

12. In an oscillation generator of the thermionic vacuum tube type, agrid circuit, a plate circuit, a frequency-determining network in saidgrid circuit comprising an inductance, a first condenser variable insteps, and a second condenser which is continuously variable for tuningsaid grid circuit, means for short-circuiting a portion of saidinductance for eifecting large changes in the frequency of the currentgenerated by said oscillation generator, feedback couplings between gridand plate of said generator and including said first condenser and aninductance electromagnetically coupled to said inductance in said gridcircuit, the two couplings together thus provided between said plate andgrid circuits being proportioned to provide a more uniform output insteps to effect large changes in the frequency of said oscillationgenerator.

14. In an oscillation generator including a thermionic vacuum tube, agrid circuit, a frequencydetermining network in said grid circuit, saidnetwork including inductance variable in steps, a first condenservariable in steps, and a second condenser which is continuously variablefor tuning said grid circuit, a feedback circuit including said firstcondenser and an inductance electromagnetically coupled to saidfirst-named inductance, and means for simultaneously varying said firstcondenser and said first-named inductance in steps to effect largechanges in the frequency of said oscillation generator, the stepvariations of said first condenser and of said inductance being soproportioned that said first condenser is more effective as a feedbackcoupling for the lower frequencies than as a feedback coupling for thehigher frequencies.

15. In an oscillation generator including a thermionic vacuum tube, agrid circuit, a frequencydetermining network in said grid circuit, saidnetwork including inductance variable in steps,. a first condenservariable in steps, and a second condenser which is continuously variablefor tuning said grid circuit, a feedback circuit including said firstcondenser and an inductance electromagnetically coupled to saidfirst-named inductance, and means for simultaneously varying said firstcondenser and said first-named inductance in steps to effect largechanges in the frequency of said oscillation generator, the stepvariations of said first condenser and of said inductance beingproportioned to cause said first condenser to serve as the principalfeedback coupling for the generation of the lower frequencies and tocause said inductance coupled to said first-named inductance to serve asthe principal feedback coupling for the generation of the higherfrequencies.

16. In an oscillation generator of the vacuum tube type, adapted togenerate oscillations throughout a wide band in frequency and includinga tube having plate and grid circuits, a frequency determining circuit,included in the grid circuit of said tube and comprising an inductance,a first capacity and a second capacity, and a feedback circuit, coupledto the plate circuit of said ,tube and comprising said first capacity,means included in said frequency-determining circuit.for continuouslyvarying the generated frequency over a narrow band, and means forchanging in steps the position of said narrow band within said wideband, said last-mentioned means comprising switching means forsimultaneously changing in,steps the inductance of saidfrequency-determining circuit and the first capacity included in bothsaid feedback and said frequency-determining circuits.

17. In an oscillation generator of the thermionic vacuum tube typeincluding a cathode and at least two additional electrodes, a frequencydetermining circuit connected between the cathode and one of saidelectrodes and comprising a. variable inductance, a capacity variable insteps, and a continuously variable capacity tuning said circuit; and asecond circuit connected between the cathode and another of saidelectrodes andincluding an inductance magnetically coupled to thefirst-mentioned inductance and including said capacity variable i steps.

18. An oscillation generator for generating a current of any frequencyin a plurality of wave bands, comprising a vacuum tube having plate,grid and cathode electrodes, a grid circuit for determining thefrequency to be generated, connected between grid and cathode, saidcircuit comprising an adjustable inductance in series with a capacityadjustable in steps, shunted by a variable condenser, a control memberfor operating said variable condenser, a feedback circuit between plateand cathode, having an inductance magnetically coupled to saidfirst-mentioned inductance, and including said adjustable capacity, andswitching means to simultaneously change the values of said adjustableinductance and said adjustable capacity.

19. An oscillation generator for generating a current of any frequencyin a plurality of wave bands, comprising a vacuum tube having plate,grid and cathode electrodes, a grid circuit for determining thefrequency to be generated, connected between the grid and cathode, saidgrid circuit comprising adjustable inductance in series with a capacityadjustable in steps, shunted by a variable condenser, a control memberfor operating said variable condenser, a feedback circuit between plateand cathode, having an inductance magnetically coupled with saidfirst-mentioned inductance, and switching means to simultaneously changethe values of said adjustable inductance and said adjustable capacity.

20. An oscillation generator of the thermionic vacuum tube typeincluding grid and plate circuits, a frequency-determiningnetwork totune one of said circuits, said network including a variable inductancea first capacity adjustable in steps, and a second capacity which isvariable; feedback means between said grid and plate circuits includinginductive reactance; uni-control means for simultaneously modifying saidvariable inductance and the value of said first capacity whereby theeffective coupling between the grid and plate circuits is maintainedsubstantially uniform throughout a broad wave band.

21. In an oscillation generator of the thermionic vacuum tube type, agrid circuit, a frequency-determining network in said circuit comprisinga. variable inductance, a first capacity variable in steps, and a secondcapacity which is continuously variable for tuning said grid circuit, afeedback circuit including an inductance electromagnetically coupled tosaid variable inductance, and means for simultaneously altering saidvariable inductance and said first capacity to effect large changes inthe frequency of said oscillator.

HAROLD MILLER LEWIS.

